The present invention generally relates to the control system art. More particularly, the present invention relates to the provision of signals for control purposes, and especially to providing double edge modulated pulse signals for control purposes in a continuously variable transmission system and system apparatus for implementing this improved technique.
Various applications and constructions for continuously variable transmission systems are set forth in the following related, copending applications filed on Mar. 13, 1987 herewith: "Temperature Compensation Technique for a Continuously Variable Transmission Control System," Ser. No. 25,392; "Ratio Control Technique for Continuously Variable Transmission Systems," Ser. No. 25,389, now U.S. Pat. No. 4,793,454; "Continuously Variable Transmission Clutch Control System," Ser. No. 25,391, now U.S. Pat. No. 4,811,225; and "Special Start Technique for Continuously Variable Transmission Clutch Control," Ser. No. 25,476. The teachings of the above identified applications are incorporated herein by reference.
Additional examples of the operation and construction of continuously variable transmissions (CVT's), may be found in U.S. Pat. No. 4,522,086, entitled "Control System for Continuously Variable Transmission" and U.S. Pat. No. 4,458,318, entitled "Control Arrangement for a Variable Pulley Transmission." All of the above identified applications and patents are assigned to the assignee of the present application.
The operation and construction of hydraulic control systems for use in CVT's are shown generally by U.S. Pat. No. 3,115,049--Moan--and U.S. Pat. No. 4,152,947--Van Deursen et al. Other still pending applications and U.S. patents provide additional improvements in the continual variable transmission art including, "Hydraulic Control System for Continuously Variable Transmission," Ser. No. 421,198, filed Sep. 22, 1982, which issued Dec. 15, 1987 as U.S. Pat. No. 4,712,453; "Hydraulic Control System for Continuously Variable Transmission," Ser. No. 717,913, filed Mar. 29, 1985; which issued Jan. 12, 1988 as U.S. Pat. No. 4,718,308; and "Clutch Control System for a Continuously Variable Transmission," U.S. Pat. No. 4,648,496, issued Mar. 10, 1987.
Those applications and patents described above which are not specifically incorporated by reference are hereby incorporated to the extent they deal with a control system regulated by means of a pulse width modulated signal.
Due to the use of control valves and the nature of the hydraulic systems utilized for various control applications in the above identified patents and applications, the operation frequency for any pulse width modulated signal utilized therein may be unduly limited. For example, in the various CVT applications mentioned above, it has been found that a pulse width modulation signal may not have an operation frequency greater than about 100 Hz because of the physical constraints of the electro-hydraulic valve system in use. It is envisioned that other control systems outside of the continuously variable transmission art may likewise share similar physical constraints. However, it may be desirable, particularly from a system response speed viewpoint, to provide an update to a digital implementation of a PWM control signal more frequently than the frequency limited by their physical constraints.